The current direction in telecommunications standards development and telecommunications product development involves the convergence of circuit-based traffic and packet-based traffic in transport equipment. This convergence requires that transport equipment support a variety of connection-oriented (CO) transport technologies, including connection-oriented, circuit-switched (CO-CS) transport technologies (e.g., Synchronous Optical Network (SONET), Optical Transport Network (OTN), and like connection-oriented, circuit-switched transport technologies) and connection-oriented, packet-switched (CO-PS) transport technologies (e.g., Multiprotocol Label Switching (MPLS) and like connection-oriented, packet-switched transport technologies).
In transport equipment design, standards bodies (e.g., International Telecommunication Union-Telecommunications (ITU-T), Internet Engineering Task Force (IETF), and like standards bodies) are currently standardizing functionality models for such transport technologies. A key challenge in transport equipment design is translation of standard functionality models specified by standards bodies into specific technology implementations. An accurate implementation of the standardized functionality models in transport equipment implementations is a key design requirement since adherence to the standardized functionality models impacts the interoperability and network behavior of the resulting transport equipment implementation.
An important class of transport equipment includes transport switches (e.g., CO-CS transport switches, CO-PS transport switches, converged transport switches, and the like), which are characterized by signal switching functionality, protection switching functionality, and like functionality. The signals processed by transport switches typically include path-layer signals (i.e., an end-to-end traffic signal from a connectivity perspective) and section-layer signals (i.e., a bundle of path-layer signals transported between transport switches using a communication link). A transport switch may support many functions, including termination/origination of section-layer signals, protection switching of section-layer signals (section protection), and protection switching of path-layer signals (path protection).
In current transport switch implementations, an ingress section-layer signal is received by an ingress port unit. The ingress port unit terminates the ingress section-layer signal (e.g., by demultiplexing the ingress section-layer signal to extract path-layer signals conveyed by the ingress section-layer signal). The ingress port unit provides the extracted path-layer signals to a switch unit. The switch unit performs path-layer switching of path-layer signals. The switch unit provides the switched path-layer signals to an egress port unit. The egress port unit originates an egress section-layer signal (e.g., by multiplexing the switched path-layer signals to form the egress section-layer signal). The egress section-layer signal is transmitted by the egress port unit. In many current transport switch implementations, the port units and switch units are physically separate.
In current transport switch implementations, a transport switch may further include non-intrusive monitoring (NIM) of path-layer signals (P-NIM). The non-intrusive monitoring of path-layer signals may include monitoring path-layer signals for faults (i.e., path-layer fault management, which may also be referred to as path-FM) and monitoring path-layer signals for performance (i.e., path-layer performance management, which may also be referred to as path-PM). The non-intrusive monitoring of path-layer signals (e.g., path-FM and path-PM) is performed by NIM functions. In some existing transport switch implementations, NIM functions are implemented only on the switch units. In some existing transport switch implementations, NIM functions are implemented only on the port units.
In some existing transport switch implementations, in which section-layer protection is implemented using separate section-layer switching, NIM functions are located after (in the direction of transmission) the section-layer switch. In other existing transport switch implementations, however, for efficiency of implementation, section-layer protection may be implemented using path-layer switching functionality. In one such implementation, a pair of port units may be associated, where the first port unit is active and the second port unit is inactive (only becoming active if section-layer protection switching becomes necessary). In such implementations, since section-layer switching is implemented using path-layer switching, NIM functions are located before (in the direction of transmission) the section layer switch.
In such transport switch implementations, in order to emulate the fact that NIM functions are located after the section-layer switch in the standards model while NIM functions are located before the section-layer switch in the actual implementation, the transport switch uses a first set of NIM functions associated with the first port unit while the first port unit is active and a second set of NIM functions associated with the second port unit while the second port unit is active (i.e., after a section-layer protection switch). In such implementations, the set of NIM functions that is active at any given time depends on the status of the section-layer selector (i.e., which may either select the first port unit as the active port unit or the second port unit as the active port unit).
In some transport switch implementations, NIM functions (including NIM functions associated with the first port and NIM functions associated with the second port) may be implemented either on the switch unit or, alternatively, on the first port unit and second port unit, respectively. The NIM functions associated with the first port unit are active while the first port unit is active (and the NIM functions associated with the second port unit are inactive while the second port unit is inactive). If the section-layer switch flips from the first port unit to the second port unit, such that the first port unit becomes inactive and the second port unit becomes active, the NIM functions associated with the first port unit switch from being active to being inactive and the NIM functions associated with the second port unit switch from being inactive to being active.
In implementations in which NIM functions are implemented on the switch unit, since the cost of providing NIM functionality is concentrated on the switch unit (rather than being distributed), the startup cost of a transport switch system is high because the transport switch system must always provide the maximum number of possible NIM functions irrespective of actual system needs. In other words, implementations in which NIM functions are implemented on the switch unit prevent pay-as-you-grow strategies.
In implementations in which NIM functions are implemented on the port units, the set of active NIM functions is transferred between port units during section-layer protection switches (often referred to as “NIM hopping”). Since NIM hopping is a complex operation requiring nontrivial, time-critical handshakes across port units in order to emulate seamless operation specified in standards models, implementations in which NIM functions are implemented on the port units are complex and, therefore, expensive.